Lungs

The lungs may be affected by S. mansoni both early and late in the infection.

In the initial phase of the disease, when the larvae pass through the lungs (the Katayama syndrome, Fig. 2.58), there is often a transient increase in lung markings, occasionally with some faint soft nodulation, more visible in the lower lobes, and enlargement of the mediastinal lymph nodes. If treatment is initiated, the reaction may be more obvious and spread throughout both lungs, probably due to an allergic alveolitis caused by reaction to the dead larvae. In either event the diagnosis of miliary tuberculosis, influenzal pneumonia, or other acute infection may be considered. Recovery is rapid and the chest radiograph will usually be normal thereafter. Although the pseudotubercles around the larvae may persist after the Katayama stage and calcify after treatment, this is not a common finding radiologically, nor does the resulting fibrosis show on the chest radiograph, though it may possibly be seen with high-resolution, thin-section CT.

Fig. 2.58. The acute larval phase of pulmonary schistosomiasis; the patient's chest x-ray had been normal 2 months earlier. There is prominence of the hila with multiple soft patchy densities throughout both lungs, particularly in the lower lobes. This corresponds to the passage of larvae through the lungs, the Katayama stage. (Courtesy of Dr. John Ebersole, Lancaster, Pennsylvania).

The clinical and radiological manifestations of schistosomiasis mansoni involving the lungs probably depend not only on the number of eggs reaching the pulmonary circulation but also on the host reaction. Granulomas are an indication of delayed hypersensitivity, and previous infections result in markedly accelerated granuloma formation (Figs. 2.59, 2.60). Immunosuppression inhibits this process. Perhaps the variable immune status of the patients accounts for the geographic variation, because severe lung changes in schistosomiasis occur in Egypt and parts of South America and the Caribbean, and yet are uncommon in many regions of Africa, despite the prevalence of the infection.

It should be emphasized again that live adult schistosomes do not cause any host response and that many immature and dead eggs similarly provoke little local response. The majority of patients with chronic schistosomiasis are asymptomatic; severe lesions are present in only a small percentage of the many millions of people who harbor this parasite. Nevertheless, in some unfortunate individuals there is eventual formation of a sufficient number of granulomas to produce anatomical and physiological alterations.

In the later phase, pseudotubercles develop in the lung parenchyma with small round cells surrounding the eggs of S. mansoni (Fig. 2.59 A-C). When numerous, these granulomas may cause a diffuse, fine reticulonodular pattern seen throughout the lungs on chest radiographs, but better demonstrated by high-resolution CT. CT is also better at demonstrating the slight interstitial fibrosis that develops in some patients, but this can also be seen on a plain chest radiograph. Endovascular localization of the eggs, with intimal thickening and obliteration of the lumen of the small arterioles and extensive inflammation and granuloma formation, is the typical pathological finding as pulmonary schistosomiasis progresses (Fig. 2.61) This can often be been on plain radiographs of the chest, as well as on CT scans. The differential diagnosis will include pneumonia, particularly eosinophilic pneumonia, and tuberculosis. In some patients a solitary pulmonary bilharzioma will resemble a tuberculoma or malignancy; there are no distinguishing features.

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Fig. 2.59 A-D. All schistosomes cause pulmonary granulomas. A A pseudotubercle in the lung parenchyma; there is a multinucleated foreign body giant cell and small round cell inflammatory reaction surrounding an egg of S. mansoni. AFIP 729756. B Another lung granuloma containing multiple eggs of S. mansoni with a similar surrounding reaction and connective tissue proliferation. AFIP 68-4761-1. C This granuloma around an S. mansoni egg has replaced the lumen and extended through the wall of a pulmonary arteriole. There is a surrounding early angiomatoid, a new channel formation which diverts the flow of desaturated blood from pulmonary arterioles into pulmonary venules, creating a right-to-left shunt, with decompression of the pulmonary arteriole system and systemic desaturation. This results in the syndrome of cyanosis with normal pulmonary artery pressure and osteoarthropathy. D Hypertrophic pulmonary osteoarthropathy with periosteal new bone formation (arrows) along the distal shafts of the femora and proximal shafts of the tibiae of a 42-year-old Egyptian, who also had schistosomal colonic polyposis. (D courtesy of Dr. Nabil Ayad El Mesery, Cairo).

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Fig. 2.60 A-D. Diffuse small nodular densities throughout both lungs due to schistosomal granulomas. The right mid-lung field of A is enlarged in B. The left lower lung field of C is enlarged in D. (Courtesy of Dr. H. Pagan-Saez, San Juan).

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Fig. 2.61 A-C. Chronic schistosomiasis mansoni damages the cardiopulmonary system. In this Puerto Rican male there is (A) diffuse fine nodulation throughout both lungs because of numerous granulomas around the eggs in the parenchyma. At this stage the heart and pulmonary artery appear normal. A few years later (B), the miliary granulomatous pattern has cleared, leaving slight interstitial fibrosis. The main pulmonary artery segment has dilated and the central pulmonary artery has become prominent, while the peripheral arteral artery pattern has decreased. This indicates secondary pulmonary hypertension. C The lung of a different patient shows a pulmonary arteriole whose lumen has been virtually obliterated by marked intimal thickening, with an intense surrounding cellular reaction and early angiomatoid formation. H & E, x196. (Courtesy of Dr. A. Chait and AJR, 1963) The diffuse endovascular, obliterative, granulomatous process blocks the pulmonary arteriole flow, which results in pulmonary arteriole hypertension, right heart strain and cor pulmonale. Both the clinical and the radiographic findings depend on the number of eggs which reach the lungs and the formation of the extensive granulomas. In advanced pulmonary schistosomiasis there will be endovascular localization of the eggs, intimal thickening, and obliteration of the vascular lumen, with extensive inflammatory and granulomatous reaction.